1. Field of the Invention
The present invention relates to a semiconductor device in which a voltage dropping circuit is arranged to drop a voltage of electric power supplied from a voltage source and to output a dropped voltage, and more particularly to a semiconductor device which can be easily connected and operated with each of various types of integrated circuits for power supply.
2. Description of Related Art
FIG. 8 is a block diagram showing the configuration of a conventional power supply system. In FIG. 8, referential numeral 101 indicates a chip of conventional semiconductor device for receiving a voltage from a voltage supply source and performing an operation by using electric power of the voltage. 102 indicates a power supply integrated circuit (hereinafter, called a power supply IC) for supplying current of a high voltage to the semiconductor device 101. 103 indicates a power supply terminal which is arranged in the semiconductor device 101 and is connected with a wire which extends from the power supply IC 102. 104 indicates an internal circuit. 105 indicates a main voltage dropping circuit for dropping the high voltage applied to the power supply terminal 103 to a prescribed voltage required to operate the internal circuit 104. 106 indicates a secondary voltage dropping circuit which has the same function as that of the main voltage dropping circuit 105. A current supplying capability and an electric power consumption rate in the secondary voltage dropping circuit 106 are smaller than those in the main voltage dropping circuit 105.
Next, an operation of the conventional power supply system will be described below.
Developments in advanced manufacturing of transistors in large scaled integrated (LSI) circuits have lead to reductions in the operation voltage of each transistor. Therefore this has resulted in difficulties with respect to applying conventional transistors which are operated at a standard operation voltage of 5V. Nowadays, integrated circuits (ICs) such as semiconductor devices are manufactured in consideration of the above-described restriction on the ICs. That is, even though it is required to apply a voltage of 5V to an input/output section of the semiconductor device 101, it is required to operate the internal circuit 104 of the semiconductor device 101 at a low voltage. Therefore, in cases where it is required to apply a voltage of 5V to an input/output section of the semiconductor device 101, one of two methods is adopted to operate the internal circuit 104 of the semiconductor device 101 at a low voltage. In the first method, as shown in FIG. 8, dropping circuits represented by the main voltage dropping circuit 105 and the secondary voltage dropping circuit 106 are arranged in the semiconductor device 101. In this case, the power supply IC 102 of one-voltage supply type can be used for the semiconductor device 101, and a manufacturing cost of the conventional power supply system can be reduced.
In general, in cases where a dropping circuit is arranged in the semiconductor device 101 according to the first method, though a manufacturing cost of the conventional power supply system can be reduced, electric power consumed in the dropping circuit is heightened. For example, in cases where an operation frequency in the internal circuit 104 is reduced to reduce electric power consumed in the internal circuit 104, parts of the internal circuit 104 are operated, and the electric power supply for the other parts of the internal circuit 104 is stopped by disconnecting the other parts of the internal circuit 104 from a power supply IC. In this case, electric power consumed in the dropping circuit is larger than that consumed in the internal circuit 104. Therefore, as shown in FIG. 8, the main voltage dropping circuit 105 and the secondary voltage dropping circuit 106 are arranged in the semiconductor device 101. The main voltage dropping circuit 105 is characterized by a high response speed for voltage change, a large current supplying capability and a large electric power consumption rate. The secondary voltage dropping circuit 106 is characterized by a low response speed for voltage change, a small current supplying capability and a small electric power consumption rate. One of these voltage dropping circuits 105 and 106 is appropriately operated.
For example, in cases where low electric power consumption is required of the semiconductor device 101, an output section of the secondary voltage dropping circuit 106 is used as a voltage supply for the internal circuit 104 to reduce electric power consumed in the main voltage dropping circuit 105. In addition, in cases where the voltage applied to the secondary voltage dropping circuit 106 by the power supply IC 102 is lowered, electric power consumed in secondary voltage dropping circuit 106 can be more reduced.
In contrast, the second method is generally adopted for an IC having no dropping circuit, and a power supply IC of two-voltage supply type is used in the second method. In this two-voltage supply type power supply IC, a voltage source of a high voltage such as 5V and a voltage source of a low voltage such as 3.3V are arranged. Electric power of the high voltage of 5V is supplied for an input/output section of a semiconductor device, and electric power of the low voltage of 3.3V is for an internal circuit of a semiconductor device. To set the two-voltage supply type power supply IC in a semiconductor device, the two-voltage supply type power supply IC has a high voltage outputting section and a low voltage outputting section. Electric power of the high voltage is supplied from the high voltage outputting section to the input/output section of the semiconductor circuit, and electric power of the low voltage is supplied from the low voltage outputting section to the internal circuit. In-this case, electric power consumed in the internal circuit connected with the low voltage outputting section is larger than that consumed in the input/output section connected with the high voltage outputting section. Therefore, a voltage dropping function is added to the low voltage outputting section to obtain a low electric power consumption rate. In contrast, even though the high voltage is dropped in the high voltage outputting section, the reduction of electric power consumption rate in the input/output section is low. Therefore, no voltage dropping function is usually added to the high voltage outputting section.
Because the conventional semiconductor device has the above-described configuration, in cases where the conventional semiconductor device 101 shown in FIG. 8 is connected with the two-voltage supply type power supply IC according to the second method, it is required to select either a connection of the high voltage outputting section (5V) of the power supply IC with the power supply terminal 103 of the semiconductor device 101 or a connection of the low voltage outputting section (3.3V) of the power supply IC with the power supply terminal 103 of the semiconductor device 101. Therefore, it is required to arrange a switch as a selecting means in the outside of the semiconductor device 101, and there is a problem that this results in increases in manufacturing costs for a power supply system composed of a (What is xe2x80x9cexe2x80x9d?) two-voltage supply type power supply IC and the semiconductor device 101. Also, in cases where the conventional semiconductor device 101 is connected with the one-voltage supply type power supply IC according to the first method or is connected with the two-voltage supply type power supply IC according to the second method, because electric power is supplied from the power supply IC 102 to the main voltage dropping circuit 105 and the secondary voltage dropping circuit 106, there is a problem that more electric power is consumed in the power supply system.
A main object of the present invention is to provide, with due consideration to the drawbacks of the conventional semiconductor device, a semiconductor device which can be easily connected to and operated with any type of power supply IC such as a one-voltage supply type or a two-voltage supply type and which is manufactured at low cost. Also, a subordinate object of the present invention is to provide a semiconductor device in which electric power consumed in both a main voltage dropping circuit and a secondary voltage dropping circuit is reduced even though the main voltage dropping circuit and the secondary voltage dropping circuit are arranged.
The main object is achieved by the provision of a semiconductor device comprising an internal circuit arranged on a chip, a main voltage dropping circuit, arranged on the chip, for dropping a first input voltage to a first dropped voltage and outputting the first dropped voltage to the internal circuit, a secondary voltage dropping circuit, arranged on the chip and having a current supplying capability and an electric power consumption rate smaller than those of the main voltage dropping circuit, for dropping the first input voltage or a second input voltage to a second dropped voltage and outputting the second dropped voltage to the internal circuit, a first power supply terminal which is arranged on the chip so as to allow connection with an external voltage source and is connected with the main voltage dropping circuit, and a second power supply terminal which is arranged on the chip so as to allow connection with the external voltage source and is connected with the secondary voltage dropping circuit.
In the above configuration, in cases where the semiconductor device is connected with a one-voltage supply type voltage source, electric power of a first input voltage is supplied from the one-voltage supply type voltage source to the main voltage dropping circuit through the first power supply terminal, electric power of the first input voltage is supplied from the one-voltage supply type voltage source to the secondary voltage dropping circuit through the second power supply terminal, and the internal circuit is operated according to current of a first dropped voltage or a second dropped voltage obtained in either the main voltage dropping circuit or the secondary voltage dropping circuit. Also, in cases where the semiconductor device is connected with a two-voltage supply type voltage source, electric power of a first input voltage is supplied from the two-voltage supply type voltage source to the main voltage dropping circuit through the first power supply terminal, electric power of a second input voltage is supplied from the two-voltage supply type voltage source to the secondary voltage dropping circuit through the second power supply terminal, and the internal circuit is operated according to electric power of a first dropped voltage or a second dropped voltage obtained in either the main voltage dropping circuit or the secondary voltage dropping circuit.
Accordingly, because the semiconductor device can be easily connected and operated with each of the one-voltage supply type voltage source and the two-voltage supply type voltage source without additionally arranging an electronic unit such as a switch, the semiconductor device can be conveniently used with each of various types of voltage sources, a power supply system composed of the voltage source and the semiconductor device can be simplified, and the semiconductor device can be manufactured at low cost.
It is preferred that the semiconductor device further comprises switching means, which is arranged in a wire extending from the first power supply terminal to the external voltage source, for electrically connecting or disconnecting the main voltage dropping circuit with/from the external voltage source through the first power supply terminal.
In the above configuration, in cases where the main voltage dropping circuit is disconnected from the external voltage source by the switching means, no electric powewr is supplied to the switching means.
Accordingly, the occurrence of leak current in the main voltage dropping circuit can be prevented, and electric power consumed in the semiconductor device can be reduced.
The main object and the subordinate object are achieved by the provision of a semiconductor device comprising a main voltage dropping circuit, arranged on a chip, for dropping a first input voltage to a first dropped voltage and outputting the first dropped voltage, a secondary voltage dropping circuit, arranged on the chip and having a current supplying capability and an electric power consumption rate smaller than those of the main voltage dropping circuit, for dropping the first input voltage or a second input voltage to a second dropped voltage and outputting the second dropped voltage, a first circuit unit of an internal circuit which is connected with the main voltage dropping circuit on the chip and is operated in cooperation with the main voltage dropping circuit, a second circuit unit of the internal circuit which is arranged on the chip and is operated in any time including a low electric power consumption time, first switching means, arranged on the chip, for selecting either a connection between the second circuit unit and the main voltage dropping circuit and a connection between the second circuit unit and the secondary voltage dropping circuit, a first power supply terminal which is arranged on the chip so as to allow connection with an external voltage source and is connected with the main voltage dropping circuit, and a second power supply terminal which is arranged on the chip so as to allow connection with the external voltage source and is connected with the secondary voltage dropping circuit.
In the above configuration, in a normal operation, a connection between the second circuit unit and the main voltage dropping circuit is selected by the first switching means, the first and second circuit units are operated according to electric power of the first dropped voltage obtained in the main voltage dropping circuit. Also, in a low electric power consumption operation, a connection between the second circuit unit and the secondary voltage dropping circuit is selected by the first switching means, the second circuit unit is operated according to electric power of the second dropped voltage obtained in the secondary voltage dropping circuit.
Accordingly, in the low electric power consumption operation, the occurrence of a leak current in the main voltage dropping circuit and the first circuit unit can be prevented when the outputting of current of the first input voltage output from the voltage source is stopped, and electric power consumed in the semiconductor device can be reduced.
It is preferred that the semiconductor device further comprises second switching means, which is arranged in a wire extending from the first power supply terminal to the external voltage source, for electrically connecting or disconnecting the main voltage dropping circuit with/from the external voltage source through the first power supply terminal, and a signal line through which a switching control signal is directly or indirectly sent to both the first switching means and the second switching means.
In the above configuration, a switching control signal indicating a normal operation or a low electric power consumption operation is simultaneously sent to both the first switching means and the second switching means through the signal line, and the selection operation of the first switching means and the connection/disconnection operation of the second switching means are simultaneously performed according to the switching control signal.
Accordingly, the change from a voltage supply form corresponding to the normal operation to a voltage supply form corresponding to the low electric power consumption operation can be reliably performed in a simplified configuration of the semiconductor device.
It is also preferred that the semiconductor device further comprises second switching means, which is arranged in a wire extending from the first power supply terminal to the external voltage source, for electrically connecting or disconnecting the main voltage dropping circuit with/from the external voltage source through the first power supply terminal, a signal line through which a switching control signal is sent to the second switching means, voltage comparing means for monitoring a voltage applied to the first power supply terminal, comparing the voltage and a prescribed threshold voltage and outputting a signal indicating a compared result, and control means, connected with the voltage comparing means, for controlling a selection operation performed by the first switching means according to the signal output from the voltage comparing means.
In the above configuration, when a switching control signal is sent to the second switching means, the connection/disconnection operation is performed in the second switching means, and the change of a voltage applied to the first power supply terminal is detected by the voltage comparing means. Thereafter, the compared result indicating the voltage change is received by the control means, and the selection operation of the first switching means is immediately performed under the control of the control means.
Accordingly, because the selection operation of the first switching means and the connection/disconnection operation of the second switching means can be almost simultaneously performed, the change from a voltage supply form corresponding to the normal operation to a voltage supply form corresponding to the low electric power consumption operation can be reliably performed in a simplified configuration of the semiconductor device.
Also, because the connection/disconnection operation of the second switching means can be monitored by the voltage comparing means, the reception of a control signal in the semiconductor device through a signal line is not required to perform the selection operation of the first switching means in synchronization with the connection/disconnection operation of the second switching means. Accordingly, the number of external terminals can be reduced in the semiconductor device.
Also, because the voltage input to the main voltage dropping circuit can be monitored, the occurrence of power supply fault in the voltage source connected with the semiconductor device can be immediately detected.
It is also preferred that the semiconductor device further comprises second switching means, which is arranged in a wire extending from the first power supply terminal to the external voltage source, for electrically connecting or disconnecting the main voltage dropping circuit with/from the external voltage source through the first power supply terminal, and voltage supply form determining means for determining a voltage supply form according to an operation state of the internal circuit and outputting a switching control signal directly or indirectly to both the first switching means and the second switching means to supply the first dropped voltage or the second dropped voltage corresponding to the voltage supply form to the internal circuit.
In the above configuration, when a voltage supply form is determined by the voltage supply form determining means according to an operation state of the internal circuit, a switching control signal indicating the voltage supply form to both the first switching means and the second switching means, and the selection operation of the first switching means and the connection/disconnection operation of the second switching means are simultaneously performed to supply the first dropped voltage or the second dropped voltage corresponding to the voltage supply form to the internal circuit.
Accordingly, because a voltage supply form appropriate to the internal circuit can be determined according to the operation state of the internal circuit, electric power consumed in the semiconductor device can be appropriately reduced. Also, because it is not required to produce a control signal in the outside of the semiconductor device, peripheral circuits of the semiconductor device can be simplified, and the semiconductor device can be manufactured at low cost.